Hallucination refers to when a person sees, smells, hears, feels or tastes something that does not exist. Hallucinations are a common clinical feature of schizophrenia, particularly auditory hallucinations where patients hear voices.

Hallucinations can occur as a result of several factors and some of these include:

• Mental illness such as dementia or schizophrenia
• Drug or alcohol abuse
• Progressive neurological conditions such as Parkinson’s disease or Alzheimer’s disease
• Visual loss leading to macular degeneration, also called Charles Bonnet syndrome

Hallucinations can also occur due to extreme tiredness or fatigue or due to a recent bereavement.

Types of hallucination

Hallucinations may take several different forms and some of these are described below:

Visual: Here, a person sees something that does not exist or sees something that does exist but sees it incorrectly.

Auditory: This is the most common form of hallucination in schizophrenics and refers to the perception of non-existent sounds. In schizophrenia, patients often hear voices talking to them but the hallucinations may also take the form of whistling or hissing, for example.

Command hallucination: This refers to when a person hears instructions that they should harm themselves or others. This is also a common symptom of schizophrenia.

Olfactory: These hallucinations involve smelling odours that do not exist. The odours are usually unpleasant such as vomit, urine or feces.

Tactile: This refers to when a person senses being touched.

Gustatory: These are hallucinations that cause a person to taste something that is not present.

Schizophrenia

Auditory hallucinations are the most common form of hallucination seen in people with schizophrenia. The patient hears voices that may be saying complimentary, critical or neutral words to them. The voices may also form a running commentary on the person’s actions and thoughts. Command hallucinations may also occur.

Auditory hallucination is also a well recognized feature of bipolar disorder and dementia, although it can occur in the absence of mental health conditions. Auditory hallucinations can be extremely distressing, although some people can learn to live with the voices, particularly if the words they hear are neutral or complimentary rather than negative. Auditory hallucination can also occur as a result of bereavement, which can lead to the person believing they can hear the voice of a loved one.

Other causes of hallucination

Some less common causes of hallucination include:

Drug-induced hallucination - The use of illicit drugs such as cocaine, LSD, amphetamines or ecstasy can cause hallucinations. Excessive alcohol consumption is another cause. These hallucinations can occur during periods of withdrawal from drugs or alcohol if the substances are stopped too suddenly. Drug-induced hallucinations are usually visual but may also involve other senses.

Hallucinations in children with fever - A high fever can sometimes cause children to hallucinate. The child should be kept well hydrated while a doctor is contacted. However, these hallucinations usually pass within a few minutes.